Surge suppression transmission means

ABSTRACT

In a coaxial connector a generally toroidal shaped member of metal oxide varistor material is connected between the inner and outer conductors of the connector. The metal oxide varistor material has an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter. The spacing of the peripheral portions of the member is set so that a high impedance is presented to normal applied voltage between the peripheral portions. For voltages applied between the peripheral portions progressively in excess of the normal voltage rapidly decreasing impedance is presented by the toroidal member in accordance with the alpha of the material thereby limiting the variation in voltage between the peripheral portions of the toroidal shaped member.

United States Patent [191 Tasca et a1.

[54] SURGE SUPPRESSION TRANSMISSION MEANS Inventors: Dante M. Tasca, Philadelphia, Pa.; John D. Harnden, Jr.; Francois D. Martzloff, both of Schenectady,

[58] Field of Search...333/97 R, 81 AB, 17, 13, 24.2, 333/2, 96, 97 S; 338/202l, 216, 220;

[56] References Cited UNITED STATES PATENTS 2,428,001 9/1947 Tubbs ..333/96 2,440,748 5/1948 Johnson... 338/21 X 2,498,335 2/1950 Hunt ..329/l62 2,548,881 4/1951 Ferrill, Jr.... 333/96 X 2,602,828 7/1952 Norton ..338/20 X 2,798,207 7/1957 Reggia t ..338/8l A 2,911,601 11/1959 Gunn et a1. 333/81 B 3,014,188 12/1961 Chester et al. ..333/98 S 3,096,494 7/1963 Jacobs et al. ....329/16l X 3,259,857 7/1966 Garstang ..333/79 [451 Jan. 16, 1973 3,426,299 2/1969 Dixon, Jr. ..333/24.2 X

3,611,073 10/1971 Hamamoto et a1. ..338/20 X 3,663,458 5/1972 Masuyama et al ..252/5 1 8 OTHER PUBLICATIONS Gunn, M. W., Wave Propagation in Rectangular Waveguide Containing a semiconducting Film Proc. IEE. Vol. 1.14 2-1967, pp. 207-210.

Primary Examiner-Eli Lieberman Assistant Examiner-Wm. H. Punter Att0rneyFrank L. Neuhauser et al.

[57] ABSTRACT In a coaxial connector a generally toroidal shaped member of metal oxide varistor material is connected between the inner and outer conductors of the connector. The metal oxide varistor material has an alpha in excess of 10 in the current density range of from 10' to 10 amperes per square centimeter. The spacing of the peripheral portions of the member is set so' 11 Claims, 13 Drawing Figures FATENTEDJAN 16 I975 SHEET 1 0F 3 SOURCE llllllll IIIIIIH I |Q IIHIIII llllllll IHIIIII IIHIIII III lo 10- IO' :0 IO' I, AMPERES SURGE SUPPRESSION TRANSMISSION MEANS The present invention relates to lines for the transmission of electrical signals from one point to another point in a system and in particular to parts of such lines referred to a connectors.

Connectors are commonly used for interconnecting electrical devices or apparatus, for example, for interconnecting a source of electrical signal to a utilization device, such as a metering or visualization device. The utilization device may include elements which are sensitive to voltages or surges of voltage exceeding a predetermined limit and susceptible to damage thereby. It is common to provide in such systems, preferably in or adjacent to the connector, filter elements for limiting device. Such filters arecommonly referred to as bulkhead filters and usually include discrete elements which are coupled to the conductors of a transmission line to provide the necessary attenuation of low and high frequency voltage surges or spurious signals. Such prior art means of surge suppression have a number of disadvantages. Substantial capacitance and inductance are introduced into the transmission line system which affects the performance of the system. The capacitance and inductance deteriorates the high frequency performance. Expressed in other words, substantial insertion loss or attenuation is introduced into the transmission line system by the discrete elements coupled into the system.

Accordingly, an object of the present invention is to provide a transmission line element which provides surge suppression without introduction of significant series inductance or shunt capacitance or signal attenuation into the transmission path of the element.

Another object of the present invention is to provide a transmission line connector which does not require any additional elements, yet which provides surge suppression in addition to its usual electrical coupling function.

Another object of the present invention is to provide a surge suppression connector which is nonresonant in operation and functions by dissipation and not by storage of surges of electrical energy.

Another object of the present invention is to provide a surge suppression connector which provides a high shunting impedance for voltages below a certain value and for progressively higher voltages rapidly progressive lower impedances.

Another object of the present invention is to provide a connector which introduces a minimum of loading of a transmission system over a broad band of frequencies yet which dissipates the energy of unwanted signals exceeding a predetermined amplitude appearing in the system.

Another object of the present invention is to provide a surge protection connector which has substantially negligibletime delay in the operation thereof in the suppression of surges.

A further object of the present invention is to provide a simple surge protection connector with capabilities of absorbing surges of considerable energy.

In carrying out the invention in one illustrative embodiment thereof, there is provided a generally cylindrical outer conductor and an inner conductor within and in spaced relationship to the outer conductor. A member is provided having a peripheral outer portion contacting the outer conductor and a peripheral inner portion contacting the inner conductor. The member is constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10' to 10 amperes per square centimeter. The spacing of the peripheral portions of the member is set so that a high impedance is presented to normal applied voltage between the peripheral portions. Accordingly, for voltages applied between the peripheral portions progressively in excess of the normal voltage applied thereto rapidly decreasing impedance is presented by the toroidal member in accordance with the alpha of the material thereby limiting the variation in voltage between the peripheral portions of the toroidal shaped member.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a block diagram of a signal transmission system useful in explaining the manner in which the invention may be used.

FIG. 2 is a sectional view of the connector of the transmission system of FIG. 1 incorporating an embodiment of the present invention.

FIG. 3 is a graph of applied voltage versus current of a specific active surge suppression element of the connector of FIG. 2 plotted on log-log coordinates.

FIG. 4 shows a front view partially in section of another embodiment of the present invention.

FIG. 5 is an end view of the embodiment of FIG. 4.

FIG. 6 shows a front view partially in section of another embodiment of the present invention.

FIG. 7 is an end view of the embodiment of FIG. 6.

FIG. 8 is a graph in log-log coordinates of the voltage versus current characteristic of a specific surge suppression element of the connector FIGS. 6 and 7.

FIG. 9 shows a series of graphs in log-log coordinates of the connectors of FIG. 2 and FIG. 6 showing the impedance versus frequency characteristics thereof as well as the impedance versus frequency characteristics of a conventional connector not incorporating the surge suppression element of the present invention.

FIG. 10 shows a front view partially in section of a further embodiment of the present invention.

FIG. 11 is a sectional view of a still further embodiment of the present invention incorporating several inner conductors.

FIG. 12 is an end view of the embodiment of FIG. 1 1.

FIG. 13 shows graphs of the electrical characteristics of three metal oxide varistor materials suitable for use in the connector devices of the present invention.

Reference is now made to FIG. 1, which shows a transmission system 10 including a source 11 of electrical signal, a utilization device or load 12 and a transmission line 13 with a connector 14 connected between the source and the load to supply electrical signal thereto. The source 11, for example, may represent an antenna which picks up a high frequency electrical signal. The transmission line I3 may be a coaxial transmission line having an outer conductor and a concentrically located inner conductor. The connector 14 is a two element device, one element 15 of which is connected to the terminal end of the transmission line 13 and the other element 16 of which is connected to the input terminals of the load 13. The connector assembly 14 includes the male member 15 and the female member 16 which are separable one from the other to facilitate making and breaking connections in the system. The load 12 may be a circuit including voltage surge sensitive transistor elements. The system may be situated in the field in the presence of spurious signals of large voltage amplitude in excess of the voltage amplitude in which the voltage sensitive devices may be safely operated. in such environment, the source 11 may pick up such voltage surges and pass them on through to the load 12 with resultant damage or destruction of the voltage sensitive elements thereof. Accordingly, it is highly desirable to provide somewhere along the transmission path protective means for filtering out or dissipating the surges of electrical energy that are passed on to the load.

1 In accordance with one embodiment of the present invention, there is shown in FIG. 2, a connector element 20 .corresponding to the connector element 16 of FIG. 1. The connector element 20v includes a generally cylindrical outer conductor 21 or shell which is threaded at one end 22 to engage mating threads in the chassis of the utilization apparatus 12. The other end of the outer conductor 21 is provided with a pair of projections 23 to engaged latches on a mating member corresponding to element of FIG. 1 and is entirely conventional. Also, provided is an elongated inner conductor 25 located within and having a longitudinal axis which is concentric with the axis of the outer cylindrical conductor 21. One end of the elongated inner conductor includes a plurality of fingers 26 defining an opening into which a corresponding inner conductor of a mating connector member (not shown) may be inserted The other end 27 of the elongated conductor 25 is connected to a terminal of the utilization apparatus 12. The inner conductor 25 is spaced and positioned within the outer conductor 21 by means of an insulating insert 28 which, for example, may be made of a material such as teflon. The insert 28 is conventional and functions to maintain the inner conductor 25 concentrically located with respect to the outer conductor 21 determines the characteristic impedance of the connector. On the shoulder 29 of the inner conductor 25 is inserted a toroidal shaped member 30 having a peripheralouter portion 31 and a peripheral inner portion 32 and alsoa pair of opposed sides 34 and 34. Preferably, the peripheral outer portion 3l'is provided with a conductive coating 35 bonded to the member 30 and similarly the inner peripheral portion is provided with a conductive coating 36 bonded thereto. The toroidal shaped member 30 is inserted in the connector such that the inner peripheral cylindrical surface thereof conductively engages the outer cylindrical surface of. the shoulder 29 and the outer cylindrical surface of the toroidal shaped member 30 conductively contacts the inner cylindrical surface of the outer conductor 21. The toroidal member 30 is held in axial position by means of a circular shoulder 40 formed in the inner portion of the outer conductor 21 which engages planar side 34 of the toroidal member and by means of the teflon insert 28 which engages the opposite planar side 33 of the toroidal member. The toroidal member 30 is constituted of a metal oxide varistor material having an alpha (a) in excess of 10 in the current density range of from l0 to 10 amperes per square centimeter. The spacing of the conductive peripheral portions 35 and 36 of the toroidal member is set so that a high impedance is presented to a normal applied voltage between the conductive peripheral portions whereby when voltages are applied between the peripheral portions progressively in excess of a predetermined normal voltage, progressively and rapidly decreasing impedance is presented by the toroidal member 30 in accordance with the alpha (a) of the material thereof thereby limiting the variation voltage between the conductive peripheral portions 35 and 36 and hence, between the inner and outer conductors of the connector 20.

The toroidal shaped member 30 is constituted of a metal oxide varistor material such as described in Canadian patent 831,691, which has a non-linear current versus voltage characteristic. The material described in the aforementioned patent is constituted of fine particles of zinc oxide with certain additives which have been pressed and sintered at high temperatures to provide a composite body of material. The current versus voltage characteristics of the composite body is expressed by the following equation:

=(v/c) (1) where V is voltage applied across a pair of opposed surfaces or planes,

I is the current which flows between the surfaces,

C is a constant which is a function of the physical dimensions of the'body as well as its composition and the process used in making it,

a is a constant for a given range of current and is a measure of the non-linearity of the current versus voltage characteristic of the body.

ln.equation (1), when V is used to denote voltage between opposed planes of a unit volume of material, or voltage gradient, current flow through the unit volumeof material in response to the voltage gradient becomes current density. For the metal oxide varistor material for current densities which are very low, for example, in the vicinity of a microampere per square centimeter, the alpha (0:) is relatively low, i.e., less than 10. lri the current density range of from 10 to 10 amperes per square centimeter, the alpha is high, i.e., substantially greater than 10 and relatively constant. In the current density range progressively in excess of 10 amperes per square centimeter, the alpha progressively decreases. When the current versus voltage characteristic is plotted on log-log coordinates, the alpha is represented by the reciprocal of the slope of the graph in which current density is represented by the abscissa and voltage gradient is represented by the ordinate of the graph. For a central range of current densities of from lO" to 10 amperes per square centimeter, the reciprocal of the slope is relatively constant. For current densities below this range, the reciprocal of the slope of the graph progressively decreases.,Also, for current densities above this range, the reciprocalof the slope of the graph progressively decreases.

The voltage gradient versus current density characteristics of three types of material in log-log coordinates are set forth in FIG. 13. Graphs 105 and 106 are materials of high voltage gradient material and graph 107 is a graph of low voltage gradient material. For all of the graphs in the current density range from to 10 amperes per square centimeter, the alpha is high and is substantially greater tan l0 and relatively constant. For densities progressively greater than 10 amperes per square centimeter, the alpha progressively decreases. For current densities progressively less than 10' the alpha also progressively decreases.

As the metal oxide varistor material is a ceramic material, the surfaces thereof may be metallized for facilitating electrical connections thereto in a manner similar to the manner in which other ceramic materials are metallized. For example, Silver Glass Frit, Du Pont No. 7713, made by the Du Pont Chemical Company of Wilmington, Delaware, may be used. Such material is applied as a slurry in a silk screening operation and fired at about 550C to provide a conductive coating on the surface. Other methods such as electroplating or metal spraying could be used as well.

The non-linear characteristics of the material results from bulk phenomenon and is bi-directional. The response of the material to steep voltage wave fronts is very rapid. Accordingly, the voltage limiting efiect of the material is practically instantaneous. I-Ieat generation occurs throughout the body of material and does not occur in specific regions thereof as in semiconductor junction devices, for example. Accordingly, the material has good heat absorption capability as the conversion of electrical to thermal energy occurs throughout the material. The specific heat of the material is 0.12 calories per degree Centigrade per gram. Accordingly, on this account, as well, heat absorption capability of the material is advantageous as a surge absorption material. The heat conductivity of the material is about one-half the heat conductivity of alumina. Accordingly, any heat generated in the material may be rapidly conducted from the material into appropriate attached heat sinks.

The material, in addition to the desired electrical and thermal characteristics described above, has highly desirable mechanical properties. The material has a fine grain structure, may be readily machined to a smooth surface and formed into any desired shape having excellent compressive strength. The material is readily molded in the process of making it. Accordingly, any size or shape of material may be readily formed for the purposes desired.

Accordingly, the toroidal member 30 is formed to the desired dimensions by either molding or by machining-from a larger body of material and electrodes or conductive coatings applied as described above. The electrodes are of a size and are spaced apart so as to provide the desired characteristic of voltage versus current. A connector of the design or configuration shown in FIG. 2 for use with a line having a characteristic impedance of 50 ohms in which the toroidal member 30 was provided with an outer diameter (surface 31) of 7 millimeters, an inner diameter (surface 32) of 2.5 millimeters and a distance between opposed sides 33 and 34 of 2.5 millimeters was connected in a system such as shown in FIG. 1 with a load impedance of 50 ohms. The

voltage versus current characteristic shown in graph 41 of FIG. 3 was obtained in which voltage between inner and outer portions of the toroidal member 30 is plotted along the ordinate of the graph and current flow between these portions is plotted along the abscissa. In the graph of FIG. 3, for a signal having an amplitude of volts, a current of one microampere flows. At this value of current the effective alpha of the connector is substantially less than 10 and as a matter of fact, is approximately 4. As signals of greater amplitude are applied, the current increases and correspondingly, the alpha of the material in that current range increases. When a current of i0 amperes flows as a result of a voltage of approximately volts being applied between the electrodes on the peripheral portions of the toroidal member, the alpha of the material is approximately IS. A continuous signal of such magnitude would generate 0.12 of a watt in the toroidal member. Such power would be readily conducted through the material to the shell or outer conductor 21 and dissipated. The higher voltage signals appearing would be substantially limited to less than 200 volts as the graph of the characteristic extends toward higher currents with only a slight rise in voltage. The important consideration to note in graph 41 is that for signals of 70 volts or less, dissipation in the connector is less than 70 microwatts which represents low standby power dissipation. If however, surges should occur of a value of volts, dissipation would rise to 1.5 watts, provided of course, the surges had low driving point impedance. Such power would be dissipated in the toroidal member and conducted to the outer conductor 21 where it would be dissipated. Unless surges were of very high power, occurred over a long interval of time and were obtained from a source of negligible impedance, any surge even in excess of approximately 200 volts would be essentially limited to the 200 volt range of the characteristic of the toroidal member.

Referring now to FIG. 9, there are shown graphs in log-log coordinates of the impedance as a function of frequency for various connectors. Graph 45 represents the impedance of a conventional connector such as shown in FIG. 2 without the surge suppression member in the absence of surge suppression members such as member 30, as a function of frequency. Graph 46 shows the impedance characteristic of connector 20 of FIG. 2 with the surge suppression member having dimensions and characteristics set forth above. As metal oxide varistor material has a relatively high dielectric constant (approximately 1800), the toroidal member 30 increases the capacitance at the point of its insertion in the connector 20. Accordingly, the graph 46 is shifted to the left and is essentially parallel with the graph 45. That is, the impedance of the connector 20 is lower in view of the fact that the capacitance thereof is higher. A certain amount of series inductance is also introduced into the connector with the inclusion of the toroidal member 30. Accordingly, at higher frequencies, resonance effects predominate and in the particular example of connector 20 described above, the resonance peak occurs near 100 Megahertz. The graph 46 instead of being a straight line, has a gradually increasing negative slope which reaches its maximum value at approximately 100 Megahertz. When the connector'20 is connected to a 50 ohm transmission line for which it was designed, and is terminated with a 50 ohm impedance, the graph 47 is obtained. Graph 47 essentially represents the paralleling of the 50 ohm terminal impedance with the impedance of the connector 20 as represented in graph 46.

The embodiment shown in FIG. 4 is directed to improve the impedance versus frequency response of the connector of FIG. 2 and still provide the desired surge protection. To this end, the shunting capacitance provided by the high dielectric constant of the metal oxide varistor material is reduced. The connector of FIG. 4 is essentially the same as the connector of FIG. 2, with the exception that a toroidal member 51 thereof is provided with electrodes on a side thereof, thereby substantially reducing the capacitance appearing in the shunt between the inner and outer conductor of the connector 50in the vicinity of the toroidal member 51. The connector 50 includes an outer shell member 52 and an inner conductor 53 member. A toroidal member 51 of metal oxide varistor material is provided on one side 55 thereof with an inner conductive ring 56 and an outer conductive ring 57. The outer conductor member 52 is provided with a circular ridge 58. Inner conductor is also provided with a cylindrical ridge 59 or shoulder. The toroidal member 51 is restrained in movement in one direction along the axis of the connector by the ridges 58 and 59. It is restrained in movement in the other direction along the axis of the connector by the insulating member 60 which also supports the inner conductor 53 in relation to the outer conductor 52. The outer ring 57 abutts against the shoulder S8'and inner ring 56 abutts against shoulder 59 on the inner conductor. In the connector of FIGS. 4 and 5 as a minimum of cross-section area is presented by the adjacent edges of the concentric ring conductors 56 and 57 and as the current flow occurs between such edges near the surface of the metal oxide varistor body 51, the capacitance at that planar region in the connector is substantially reduced, thereby substantially improving the impedance versus frequency characteristic of the connector while atthesame time providing the desiredprot ection againstvoltage surges from appearing at the output terminals of'the connector.

' Referenceis now made to FIGS. 6 and 7 which show another'embodiment of a connector 65 in accordance with the present invention for substantially reducing the capacitance'introduced into the connector by the metal oxide varistor protective body thereof. In the connector 50 of FIGS. 4 and 5, unless the spacing between the adjacent edges of the ring conductors 56 and 57 is maintained to closetolerances, current conductionbetween the ring conductors 56 and 57 is nonuniform with resultantinefficient use being made of metal oxide varistor material. That is, certain sectors of the space between the conductors will conduct substantially morecurrent than other sectors. This will be readily understood by considering the voltage versus current characteristics of the material. Let it be assumed that for two sectors of the metal oxide varistor material between the ring conductors of FIGS. 4 and 5, the spacing between the inner and outer concentric ring is different. For one sector, a voltage versus current graph such as shown in FIG. 3 would exist. For the other sector for which the spacing is less, a voltage versus current'graph substantially identical to the voltage versus current graph of the first sector would exist, however, it would be displaced downward along the ordinate of the coordinate system from the graph of the first sector. Accordingly, fora given voltage appearing between the inner and outer ring conductors 56 and 57, the sector with the smaller spacing would carry substantially greater currents in a region where the graphs are relatively flat as a line drawn through the given voltage and parallel to the abscissa would be nearly parallel to graphs. To maintain uniform current distribution while at the same time maintain reduced capacitance, the inner and outer ring conductors have the form shown in FIGS. 6 and 7 to which reference is now particularly made. Elements of FIGS. 6 and 7, identical to elements of FIGS. 4 and 5 are identically designated. The inner ring conductor 66 is provided with four projections 67, 68, 69 and 70, equally spaced about the ring conductor. The edges of each of the projections are of equal length, equally spaded from the central axis of the connector and terminated in straight edges. The inner edge of outer is conductor provided with four straight edges 76, 77,78 and 79, each parallel to a straight edge of a respective projection and equally spaced from the central axis of the connector. Accordingly, a ring conductor arrangement is provided in which over each of four quadrants or sectors of the metal oxide varistor body, the identical spacing occurs between inner and outer ring conductors 66 and 75.

A connector assembly such as shown in FIGS. 6 and 7 utilizing metal oxide varistor material wafer having a .voltage gradient of 200 volts per millimeter at a current density of one milliampere per square centimeter was constructed. The connector was provided with terminal straight edges of one millimeter in length for the projections from the inner conductive ring. A gap spacing of l millimeter between a straight edge of a projection and a corresponding straight edge of an outer conductive ring was also provided. The voltage versus current response of the connector is shown in graph of FIG. 8 to which reference is now made. In this figure, voltage between inner conductor 53 and outer conductor 52 is plotted along the ordinate and current flow through the toroidal member 54 is plotted, along the abscissa of log-log coordinates. For signals of 100 volts or less, the current flow through the toroidal member 54 is less than one-hundredth of a microampere. As the voltage and energy of the signal increases, current increases, and for a voltage of 400 volts across the toroidal member, a current of l microamperes flows. For voltages across the toroidal member in excess of 400 volts, the current increases rapidly for slight increases of voltage fFor a voltage of 600 across the toroidal member one-hundredth of an ampere flows throughthe member. The alpha of graph 80 in'the range from'l microampere to 0.01 amperes is of the order of 20. Accordingly, it is readily apparent that for surges of signal even of considerable power and energy content, the voltage appearing at the output of the connector is essentially limited to a low value. In connection with the cross-pattern design of the inner conductive rings of the toroidal member, should the spacing of one of the four gaps between the inner ring conductor 66 and outer ring conductor 75 be 10 percent less than the others, the metal oxide varistor material in that quadrant would take percent of the total current flow, assuming, of course, that the region of the current characteristic in which the material is operated is in the range in which the alpha is of the order of 20. It should be noted that a discrepancysuch as percent in the spacing in one of the gaps does not materially effect the overall capacitance between the inner ring conductor and the outer ring conductor. However, unless the gaps are all spaced to close tolerances, the advantage of such an arrangement in equalizing current flow is illusory. It should be recognized that while four gaps have been shown, other electrode configurations are readily apparent in which two gaps are used or three or a greater number then four. However, when a larger number of gaps are utilized, it should be noted that unless all of the gaps are precisely dimensioned, equalization of current flow in the metal oxide varistor member will not be achieved. For the larger number of gaps, inner ring conductor 66 and outer ring conductor 75 must be formed to closer tolerances than for a smaller number of gaps. With a large number of gaps, the

- problem of maintaining close tolerances in the gaps to achieve uniform current becomes as difficult as with the concentric ring conductors of FIGS. 4 and 5.

The impedance versus frequency characteristic for the specific connector of FIGS. 6 and 7 described above is shown in graph 81 of FIG. 9. As the capacitance of the connector of FIGS. 6 and 7 was substantially reduced over the capacitance of the connector of FIGS. 4 and 5, the essentially flat characteristic of impedance versus frequency was extended out to close to 100 Megahertz.

Reference is now made to FIG. 10 which shows another embodiment of the connector similar to the connectors of FIGS. 4 and 6. Elements of FIGS. 6 and 7, identical to elements of FIG. 4 are identically designated. In order to reduce the capacitance introduced by the connector and improve the high frequency response of the connector, a minimum of metal oxide varistor material is utilized. In this embodiment, a toroidal ceramic substrate 85 is provided made of a material such as alumina which has a low dielectric constant, substantially lower than that of the metal oxide varistor material. A toroidal shaped wafer 86 of metal oxide varistor material is bonded on the toroidal substrate by a suitable bonding agent such as epoxy. Concentric ring conductors are provided as shown in FIGS. 4 and 5. In other respects, the connector of FIG. 10 is identical to the connector of FIG. 4. The cross pattern of the conductive rings of FIGS. 6 and 7 could, of course, also be applied to the wafer 86. As pointed out, the advantage of providing a toroidal member in which the bulk of the toroidal member is a material of low dielectric constant is that the capacitance is substantially reduced, thereby further improving the high frequency response of the connector, while at the same time, preserving the surge protection characteristics of the device. With a reduced amount of metal oxide varistor material being utilized in the toroidal member, it should be noted that the dissipation capabilities of the toroidal member of metal oxide varistor material are reduced. While the composite toroidal member will reduce the voltage appearing at the output of the connector, it will not handle as much energy as a larger body of metal oxide varistor material.

Reference is now made to FIGS. 11 and 12 which I show a connector in which a plurality of inner conductors are provided. The connector includes an outer shell 91 and a pair of elongated inner conductors 92 and 93. A circular metal plate 94 is provided with a pair of openings 95 and 96. Metal plate 94 is supported in the outer shell. A pair of toroidal members 97 and 98 of metal oxide varistor material are provided. Each of the toroidal members 97 and 98 has an outer metallized peripheral surface and an inner metallized peripheral surface. The outer peripheral surfaces of each toroidal members 97 and 98 are dimensioned to snugly fit into a respective aperture in the plate 94. The inner surface of each of the metal oxide varistor members 97 and 98 is dimensioned to receive a respective one of the elongated inner conductors 92 and 93. The plate member 94 may be soldered in place in the connector or may be appropriately positioned by means of the insulator members 101 and 102. One insulating member 101 contacts one of the opposed sides of the plate 94 and the other insulating member 102 contacts the other of the opposed sides of the plate. The material of the plate is selected to have a coefficient of thermal expansion similar to the coefficient of expansion of glass. Accordingly, many of the materials utilized for making glass-to-metal seals and having coefficients of expansion comparable to that of glass would be suitable for use in the connector. For example, the plate 94 and the conductors 92 and 93 may be made of molybdenum or of any of a number of metal alloys of iron, nickel and cobalt which have a coefficient of expansion equal or similar to the coefficient of expansion of glass. In the arrangement of FIGS. l1 and 12, the metal oxide varistor toroidal members provide the surge protection of voltage surges occurring between each of the elongated conductors and the outer conductor and of course, between the elongated conductors as well. It will be understood that connectors with more than two inner conductors could be readily provided in accordance with the construction set forth in the embodiment of FIGS. 11 and 12.

While the invention has been described in specific embodiments, it will be appreciated that modifications may be made by those skilled in the art and we intend by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A section of transmission line comprising:

a generally cylindrical outer conductor,

an inner conductor within and in spaced relationship to said outer conductor,

a member having a peripheral outer portion contacting said outer conductor and a peripheral inner portion contacting said inner conductor,

said member being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 to 10 amperes per square centimeter, the spacing of said peripheral portions being set so that a high impedance is presented between said peripheral portions when normal voltages appear between said peripheral portions and when voltages in excess of the normal voltage progressively appear thereacross a rapidly decreasing impedance is presented by said member in accordance with the alpha of the material of said member thereby limiting the variation in voltage between the peripheral portions.

2. The combination of claim 1 in which said outer and inner peripheral portions are cylindrical.

3. The combination of claim 1 in which said member is generally toroidal shaped.

4. The combination of claim 1 in which said outer conductor is concentric with said inner conductor.

5. The combination of claim 1 in which said inner conductor is elongated.

6. The combination of claim 1 in which said member supports said elongated inner conductor in spaced relation to said outer conductor.

7. The combination of claim 1 in which said member is provided with a side surface which is substantially planar, an inner conductive ring and an outer conductive ring concentrically located on said side surface, said inner conductive ring in conductive contact with said inner conductor, said outer conductive ring in conductive contact with said outer conductor, the adjacent edges of said ring being uniformly spaced in said side surface.

8. The combination of claim 1 in which said member is provided with a side surface which is substantially planar, an inner conductive ring and an outer conductive ring concentrically located on said side surface, said inner conductive ring in conductive contact with said conductor, said outer conductive ring in conductive contact with said outer conductor, said inner conductive ring having a plurality of projections, each extending radially outward and terminating in a straight edge, said outer conductive ring having a plurality of straight edges located in the inner edge thereof, each of said straight edges of said outer conductive ring parallel to and equally spaced from a respective straight edge of said inner conductive ring.

. 9. The combination of claim 8 in which said projections are four in number equally spaced about the periphery of said inner conductive ring.

10. A section of transmission line comprising:

a generally cylindrical outer conductor,

a pair of inner conductors within and in spaced relationship to said outer conductor,

a pair of toroidal shaped members, each having a said members being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 to 10 amperes per square centimeter, the spacing of said peripheral portions of each of said members being set so that a high impedance is presented between the peripheral portions of each of said members when normal voltages appear between the peripheral portions and when voltages in excess of normal voltages progressively appear thereacross progressively decreasing impedance is presented by said member in accordance with the alpha of the material of said member thereby limiting the variation in voltage between the peripheral portions. l 1. A section of transmission line comprising: a generally cylindrical outer conductor, an inner conductor within and in spaced relationship to said outer conductor,

support member of insulating material having a cylindrical outer portion and a cylindrical inner portion and a pair of major opposed faces, a layer of metal oxide varistor material bonded to one of said faces, an outer peripheral portion of said layer conductively connected to said outer conductor and an inner peripheral portion of said layer conductively connected to said inner conductor,

said layer being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current densityrange of from 10' to 10 amperes per square centimeter, the spacing of said peripheral portions being set so that a high impedance is presented between said peripheral portions when normal voltages appear between said peripheral portions and when voltages in excess of normal voltage progressively appear thereacross, a rapidly decreasing impedance is presented by said layer in accordance with the alpha of the material thereof thereby limiting the variation in voltage between the peripheral portions. 

1. A section of transmission line comprising: a generally cylindrical outer conductor, an inner conductor within and in spaced relationship to said outer conductor, a member having a peripheral outer portion contacting said outer conductor and a peripheral inner portIon contacting said inner conductor, said member being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter, the spacing of said peripheral portions being set so that a high impedance is presented between said peripheral portions when normal voltages appear between said peripheral portions and when voltages in excess of the normal voltage progressively appear thereacross a rapidly decreasing impedance is presented by said member in accordance with the alpha of the material of said member thereby limiting the variation in voltage between the peripheral portions.
 2. The combination of claim 1 in which said outer and inner peripheral portions are cylindrical.
 3. The combination of claim 1 in which said member is generally toroidal shaped.
 4. The combination of claim 1 in which said outer conductor is concentric with said inner conductor.
 5. The combination of claim 1 in which said inner conductor is elongated.
 6. The combination of claim 1 in which said member supports said elongated inner conductor in spaced relation to said outer conductor.
 7. The combination of claim 1 in which said member is provided with a side surface which is substantially planar, an inner conductive ring and an outer conductive ring concentrically located on said side surface, said inner conductive ring in conductive contact with said inner conductor, said outer conductive ring in conductive contact with said outer conductor, the adjacent edges of said ring being uniformly spaced in said side surface.
 8. The combination of claim 1 in which said member is provided with a side surface which is substantially planar, an inner conductive ring and an outer conductive ring concentrically located on said side surface, said inner conductive ring in conductive contact with said conductor, said outer conductive ring in conductive contact with said outer conductor, said inner conductive ring having a plurality of projections, each extending radially outward and terminating in a straight edge, said outer conductive ring having a plurality of straight edges located in the inner edge thereof, each of said straight edges of said outer conductive ring parallel to and equally spaced from a respective straight edge of said inner conductive ring.
 9. The combination of claim 8 in which said projections are four in number equally spaced about the periphery of said inner conductive ring.
 10. A section of transmission line comprising: a generally cylindrical outer conductor, a pair of inner conductors within and in spaced relationship to said outer conductor, a pair of toroidal shaped members, each having a peripheral outer portion contacting said outer conductor and each having a peripheral inner portion contacting a respective one of said inner conductors, said members being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter, the spacing of said peripheral portions of each of said members being set so that a high impedance is presented between the peripheral portions of each of said members when normal voltages appear between the peripheral portions and when voltages in excess of normal voltages progressively appear thereacross progressively decreasing impedance is presented by said member in accordance with the alpha of the material of said member thereby limiting the variation in voltage between the peripheral portions.
 11. A section of transmission line comprising: a generally cylindrical outer conductor, an inner conductor within and in spaced relationship to said outer conductor, a support member of insulating material having a cylindrical outer portion and a cylindrical inner portion and a pair of major opposed faces, a layer of metal oxide varistor material bonded to one of said faces, an outer peripheral portion of said layer conductively connected to said outer conductor and an inner peripheral portion of said layer conductively connected to said inner conductor, said layer being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter, the spacing of said peripheral portions being set so that a high impedance is presented between said peripheral portions when normal voltages appear between said peripheral portions and when voltages in excess of normal voltage progressively appear thereacross, a rapidly decreasing impedance is presented by said layer in accordance with the alpha of the material thereof thereby limiting the variation in voltage between the peripheral portions. 